1. Field of the Invention
The present invention generally relates to folding sheet material and, more particularly, to a sheet folding apparatus using fold rollers arranged longitudinally with respect to a fold blade.
2. Background Information
A system for finishing printed sheets into booklets is described in PCT Document No. WO 00/18583 (hereafter referred to as “the Trovinger PCT”), hereby incorporated by reference in its entirety. The Trovinger PCT includes an operation where individual booklet sheets are folded using two drive motor assemblies. A first vertical drive motor assembly operates to immobilize a sheet by pressing it against a fold blade with a folder assembly. This first vertical drive motor assembly moves a set of fold rollers into contact with both the sheet and a longitudinal fold blade. The axes of rotation for the fold rollers are perpendicular to the fold blade used to fold each sheet. A second horizontal drive motor then operates to deform the sheet against the fold blade by reciprocating the set of fold rollers, which have been placed into contact with the sheet, back and forth along the fold blade to in effect crease the sheet. The number and spacing of these fold rollers are such that during horizontal movement of the fold rollers, at least one fold roller passes over every point along the portion of a sheet where a fold is to be formed.
The system described in the Trovinger PCT uses two separate motors to establish linear motion of fold rollers in two axes to create a fold. The time required to create a fold is the cumulative time of moving a folder assembly vertically and moving the fold rollers horizontally to crease the sheet.
Another folder apparatus is disclosed in U.S. Pat. No. 4,053,150 (Lane), hereby incorporated by reference in its entirety, which is directed to the prevention of corner dog-earring. The Lane patent includes a blade for forcing once-folded paper (e.g., a folded stack of newsprint) between a pair of rollers, thus creating a quarter-fold in the paper. Air flow jets and plates are used in the Lane patent to prevent bending of the paper edges and corners. However, the Lane patent is not capable of making precise, sharp folds and of ensuring proper paper alignment during a fold process.
It would be desirable to reduce the apparatus cost and the time required to form a precise fold in a sheet.